Objective: To use the natural experiment of health insurance reform in Massachusetts to study the impact of increased insurance coverage on ICU utilization and mortality.
Design: Population-based cohort study.
Setting: Massachusetts and four states (New York, Washington, Nebraska, and North Carolina) that did not enact reform.
Patients: All nonpregnant nonelderly adults (age 18–64 yr) admitted to nonfederal acute care hospitals in one of the five states of interest were eligible, excluding patients who were not residents of a respective state at the time of admission.
Measurements: We used a difference-in-differences approach to compare trends in ICU admissions and outcomes of in-hospital mortality and discharge destination for ICU patients.
Main Result: Healthcare reform in Massachusetts was associated with a decrease in ICU patients without insurance from 9.3% to 5.1%. There were no significant changes in adjusted ICU admission rates, mortality, or discharge destination. In a sensitivity analysis excluding a state that enacted Medicaid reform prior to the study period, our difference-in-differences analysis demonstrated a significant increase in mortality of 0.38% per year (95% CI, 0.12–0.64%) in Massachusetts, attributable to a greater per-year decrease in mortality postreform in comparison states (–0.37%; 95% CI, –0.52% to –0.21%) compared with Massachusetts (0.01%; 95% CI, –0.20% to 0.11%).
Conclusion: Massachusetts healthcare reform increased the number of ICU patients with insurance but was not associated with significant changes in ICU use or discharge destination among ICU patients. Reform was also not associated with changed in-hospital mortality for ICU patients; however, this association was dependent on the comparison states chosen in the analysis.